The same, but different...... which was the point, right? Basically means an
engine can be rated without measuring torque.

Sorta works the same for Torque, thats why they usually pair each one with
an RPM.

No one claimed one was more important than the other except you. Fact is,
the two cannot be separated, nor can they happen without RPM and get
anything done.

Those dynos measure output, be it torque or kW. Hydrualic dynos measure
torque, electric dynos measure kW output.

Inertial dynos (Dynojet, for example) don't...  they measure power (be it HP
or KW), and interpret torque based on engine RPM.  This is why a lot of
times, diesel guys only get HP ratings from their dyno runs - becuase they
don't feel like setting up the cumbersome little optical sensor to read RPM
from the engine.

Yep - and back to my F1 example...   270ft.lbs. at 8000RPM in a 3.0L V10
makes 411HP, where that same 270ft.lbs. at 2800RPM in a 4.7L V8 only makes
144HP.  Which engine's going to move the same amount of weight faster?

What's this for? It's to show that a horsepower number alone does not
accurately describe the ability an engine has to do work.

You said "If it takes 100ftlbs to turn a shaft, one shaft will turn 6 times
as fast, meaning more work is done."
We'll use that same shaft again comparing the two 100 horsepower engines.

The engine that makes 100 hp @ 1,000 rpm has 525 lbs/ft of torque. That's
plenty of torque to do the job. In fact it can run 5 shafts each requiring
100 lbs/ft of torque all at the same time. The engine that produces 100 hp @
10,000 rpm makes less than 53 lbs/ft of torque. If it takes 100 lbs/ft of
torque to turn the shaft, it will not be able to turn the shaft at all. No
work is being done.

I'll give you another example. Say I'm out shopping for a new push mower. I
get frequent rain and one corner of my back lawn doesn't drain very well.
The lawn is always wet there and the grass grows very fast. My old mower cut
fine everywhere in my lawn, including the high wet grass. It had a good 5
horsepower engine when new but now it's old and uses too much oil. I leave a
trail of smoke behind every pass. I assume any 5 horsepower push mower with
the same size blade will work the exact same way, so that's what I go
shopping for. I want a brand new mower just like my old one, but the old
model is discontinued. I find the same brand mower with the same 21" blade,
a 5hp engine, and rear mounted collection bag. Same thing as the old one
right? Well, no. It looked the same and had all the same advertised
specifications, but it wasn't the same thing. I didn't realize that my old
mower was rated 5 horsepower @ 500 rpm and the new one is 5 horsepower @
1,000 rpm. The grass doesn't really care if it gets whacked by a blade
spinning around at 500 rpm or 1,000 rpm, so the end result should be the
same. It should make tall grass short.
I try out my new mower. I get the front lawn done and it looks very nice.
That 1,000 rpm mower cuts the lawn very cleanly and deposits much more of
the clippings into the bag than my old mower ever did. I'm very happy with
my new mower even though I still don't know about the higher blade speed. I
assume the old engine was getting weak and this new one is more powerful.
Now I go around back. I get three feet into the wet high grass and the mower
stalls. I have to drag it back out of the wet area to get it started again.
I push it another three feet into the wet grass and it stalls again. It
takes me hours longer with this new mower to cut the wet area than it did
with my old mower. 5 horsepower isn't always exactly the same as 5
horsepower. The old mower had twice the torque that my new mower has. The
new mower has twice the blade speed that the old mower had.
Which one gets more work done? If you ask the guy that has to push the mower
through the tall wet grass, it's the old one.

I'm not saying that horsepower ratings are meaningless. I'm only saying that
horsepower ratings are less meaningful without an rpm to go along with them.